Method for distinguish failure modes in an APC circuit and an optical transmitter using the same
AssigneeSumitomo Electric Industries, Ltd.
InventorHiroto Ishibashi
Life of this patent
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Abstract
The present invention provides an optical transmitter that enables to distinguish failure modes of the auto-power control (APC) of the laser diode (LD). The transmitter provides the APC circuit comprised of the driver for supplying the driving current, the LD, the PD for monitoring a portion of the output light from the LD, and the control unit for setting the driving current. The control unit monitors, at regular intervals, the bias current to the LD and the time differential of the bias current. The control unit only stops the APC circuit when both the bias current and the time differential of the bias current exceed respective references.
Claims10
An optical transmitter, comprising:
- a semiconductor laser diode that emits an optical signal;
- a driver that provides a driving current for the laser diode;
- a photodiode configured to sense a portion of the optical signal emitted from the laser diode and to generate a sensing signal corresponding to the portion of the optical signal;
- and
- a control unit configured to provide a control signal to the driver based on the sensing signal to keep the sensing signal constant,
- wherein the control unit is configured to monitor the driving current at regular intervals to generate a monitoring signal corresponding to a magnitude of the driving current and a time differential of the monitoring signal, to compare the monitoring signal with a first reference and the time differential of the monitoring signal with a second reference, to set an alarm when the monitoring signal exceeds the first reference, and to set the control signal so as to stop a supply of the driving current to the laser diode when the monitoring signal exceeds the first reference and the time differential of the monitoring signal exceeds the second reference.
A method for controlling an auto-power control for a semiconductor laser diode installed in an optical transmitter, the auto-power control being configured by the laser diode, a photodiode for monitoring an optical output from the laser diode, a driver for providing a driving current to the laser diode, and a control unit configured to compare the optical output with a reference and to generate a control signal so as to become the optical output substantially equal to the reference, the driver setting the driving current based on the control signal output from the control unit, the method comprising steps of:
- (a) monitoring the driving current at regular intervals;
- (b) comparing a magnitude of the driving current with a first reference, and a time differential of the driving current with a second reference;
- (c) setting an alarm when the magnitude of the driving current exceeds a first reference;
- and
- (d) setting the control signal by the control unit so as to stop the driving current when the magnitude of the driving current exceeds the first reference and the time differential of the driving current exceeds a second reference.
Dependencies are inferred from the claim text.